Abstract:
Greywater is the wastewater that results from laundry, kitchen sinks, dishwashers,
bathtubs, showers and hand basins. Greywater can be segregated from backwater
and can be treated easily for reuse in irrigation, carwash, or toilet flushing. It provides
an interesting alternate of fresh water especially in water scarce areas. Greywater
having low strength of contaminants can be treated and reused effectively by using
physicochemical treatment systems. The objective of this study was to design a
greywater recycling and reuse system at IESE, NUST, and evaluate the system
performance to produce a treated effluent quality that meets the greywater toilet
flushing reuse standard. Two sources of greywater: Boys Washroom at IESE, NUST
and Ghazali Boys Hostel, NUST were studied. The treatment system targeted the
removal of suspended particles and organic content followed by disinfection by
chlorine. Based on the results, average daily greywater production was equal to 85
gallons per day and the greywater quality was fairly low strength. Vertical Pressure
Sand Filter contributed to the 80% removal of the suspended particles while the
overall greywater treatment system efficiently removed up to 90% of the turbidity and
TSS for both greywater sources. The organic content removal in the form of BOD
and COD was 80% which was majorly achieved through Granular Activated Carbon
Filter. The optimum disinfectant dosage was selected as 11 mg/L of chlorine at
which the residual chlorine was >1 mg/L after 30-minute contact time and no Total
Coliform growth were observed for the period of four days. The saved water is
sufficient for up to 5,200 flushes in case of older toilets and 10,000 flushes in newer
toilets in a year. Greywater reuse for toilet flushing can be considered a potential
sustainable solution to water shortages experienced in a water-stressed country like
Pakistan.
